ZINC AND CADMIUM MOBILITY IN SAND - EFFECTS OF PH, SPECIATION, CATION-EXCHANGE CAPACITY (CEC), HUMIC-ACID AND METAL-IONS

This study was undertaken to investigate the ways in which pH, speciat ion, cation exchange capacity (CEC), humic acid and added metals influ ence Zn and Cd mobilities in porous media The studies were conducted u sing columns of pure sand and sand in admixture with goethite. The mob ile phases were based on aqueous NaCl solution. In all cases Zn and Cd were found to be more mobile at pH = 4.0 than pH = 6.5. Speciation ca lculations were used to rationalise all the observations. Introduction of a small amount of goethite in the column packing caused increased retardations. However the observed increases could not be explained si mply in terms of an increased column CEC value, sorption dynamics were also involved. Increased retardations were also noted in the presence of HA. The effect reflected the amounts present in the stationary and mobile phases. Ca and Fe enhanced Zn and Cd mobilities but Al had no discernible effect. (C) 1998 Elsevier Science Ltd. All rights reserved .